Field of the Invention
The subject application generally relates to an antenna system, and more specifically, relates to an antenna system for use in a mobile communication device.
Description of the Related Art
In a communication system, if a transmission antenna and a reception antenna have different polarization directions, the transmission efficiency may be negatively affected very much. For example, if the transmission antenna is horizontally-polarized, the reception antenna should be also horizontally-polarized to achieve the maximum transmission efficiency. Otherwise, a vertically-polarized reception antenna may not receive any horizontally-polarized signal at all. Also, if the transmission antenna is RHCP (Right-Hand Circularly-Polarized), the reception antenna should be also RHCP to achieve the maximum transmission efficiency. Otherwise, an LHCP (Left-Hand Circularly-Polarized) reception antenna may not receive any RHCP signal at all.
When the communication system is applied to video streaming, gaming or data transfer, the transmission data should be compressed due to there being no sufficient transmission bandwidth. However, the compressed data have some disadvantages, for example, distortion, low quality, transmission delay, and package loss, etc. For uncompressed video transmission at low frequency (e.g., 5 GHz), such as through WHDI (Wireless Home Digital Interface), it requires at least four antennas to transmit a 1080P video. This design is too large to be used in a cellular phone. Accordingly, how to design a small antenna with adjustable polarization is a critical challenge for current antenna designers.